Methods of backing up a storage apparatus include creating a duplicate in an enclosure of the storage apparatus, and backing up the duplicate in a tape apparatus located outside of the storage apparatus. With the former method involving creating a duplicate in the enclosure of the storage apparatus, restoring operations is difficult when a fault occurs in the enclosure.
In addition, remote copy functions are known which involve, in preparation of data loss in the event of a disaster such as an earthquake or fire, a plurality of storage apparatuses respectively arranged at a plurality of sites multiplexing data and storing the multiplexed data.
Remote copy functions can be roughly divided into two, namely, “synchronous remote copy” in which a storage apparatus transfers data to a copy destination storage apparatus in synchronization with a write command from a host computer, and “asynchronous remote copy” in which the storage apparatus transfers data to the copy destination storage apparatus after a completion response to the write command from the host computer.
Whichever remote copy function is used, when a disaster strikes at a primary site, operations of both the host computer and the storage apparatus are switched to a secondary site. Accordingly, data loss and suspension of operations can be minimized even when a disaster strikes at a site. In addition, recently, there is much attention on implementations aimed at avoiding a disaster when the disaster can be predicted as in the case of a typhoon or a tsunami by switching operations to a secondary site before the disaster strikes in order to prevent data loss and suspension of operations in advance.
Furthermore, since synchronous remote copy has an advantage in that data of a copy source and data of a copy destination are constantly synchronized but a response to write by a host computer disadvantageously takes time, asynchronous remote copy is generally used between sites separated by large distances.
PTL 1 discloses a technique for performing asynchronous remote copy using a journal. Upon receiving a write command, a copy source storage apparatus at a primary site writes data into a data write volume, writes journal data into a journal volume, and returns a response to a host computer. A copy destination storage apparatus at a secondary site reads journal data from the journal volume of the copy source storage apparatus asynchronously with the write command and stores the journal data in its own journal volume. In addition, the copy destination storage apparatus reflects data on a copy destination data write volume based on the stored journal data.
In addition, in PTL 2, synchronous remote copy is performed between a copy source volume of a primary site and a copy destination volume of a secondary site to duplex data. With the disclosed technique, by providing a host computer with both the copy source volume and the copy destination volume as volumes having a same identifier, accepting access at the primary site during normal operations and switching access to the secondary site upon occurrence of a fault enables the secondary site to be used transparently with respect to the host and operations to be continued without any suspension.